1. Field of the Invention
Exemplary embodiments of the present invention relate to a method of estimating a channel in a wireless communication network using the IEEE 802.11ad communication standard, and more particularly, to a method of estimating a channel, which can determine a channel environment and actively select a channel estimation scheme according to the determined channel environment, and correctly estimate the channel while reducing the amount of computation by selectively using a pilot channel estimation value only in a pilot estimation period and adjacent pilot estimation periods when the channel changes severely, i.e., when a deep hole occurs, in the pilot estimation period although an LTF channel estimation value is used.
2. Description of Related Art
With the advancement in smart devices such as a smart phone, a tablet computer and the like, the modern society enters into a highly information-oriented society. Accordingly, techniques for transmitting various types of digital information to a desired user in a speedy way are required. As digital image media techniques are advanced and the demand on high-speed wireless transmission are increased, a lot of studies on giga-bit level wireless transmission are in progress both domestically and internationally, and the most spotlighted technique among these is the IEEE 802.11ad communication standard which uses a frequency band of 60 GHz. The reason for this is that the IEEE 802.11ad communication standard can utilize a broad bandwidth of 7 GHz (between 57 GHz and 64 GHz in Korea) although this band is an industrial scientific medical (ISM) band.
However, since the 60 GHz band has a severe signal attenuation in a standby state, it recently attracts attention as a frequency band appropriate for a short range wireless network of a range of less than 10 meters. Although there are presently short range communication methods such as Bluetooth and the like, they cannot transmit a high-volume data such as a multimedia data due to the narrow bandwidth. Contrarily, the IEEE 802.11ad communication standard using a 60 GHz band enables multimedia communication of high-volume data in the field of short range data transmission.
In a wireless communication system, a lot of distortions occur in the size and phase of a data due to multiple paths of a channel. Particularly, the IEEE 802.11ad communication standard invites severe inter-symbol interference (ISI) since it uses a broad bandwidth of 7 GHZ. Accordingly, an Orthogonal Frequency Division Multiplex (OFDM) scheme is used to remove the ISI to the maximum. The OFDM is a method of dividing a broadband signal into a plurality of sub-carriers orthogonal to each other and transmitting the sub-carriers in parallel, and it has an effect of changing the characteristics of a frequency selective fading channel to the characteristics of a flat fading channel. Accordingly, the effect of the ISI can be greatly reduced.
However, although the OFDM is used, a lot of distortions occur in the size and phase of a data in the channel environment of IEEE 802.11ad communication standard. Therefore, the original signal is restored by compensating the size and phase of a distorted signal, and this process is referred to as equalization. In addition, changes in the size and phase of the signal are required to be estimated for the purpose of the equalization, and this process is referred to as channel estimation.
The channel estimation method of the OFDM is largely divided into a long training field (LTF)-based channel estimation method using training sequences and a pilot-based channel estimation method using pilot sub-carriers. Although the LTF-based channel estimation method is advantageous in that a channel can be estimated with a small amount of computation, accuracy of the channel estimation is low, whereas although the pilot-base channel estimation has a large amount of computation, accuracy of the channel estimation is excellent. Therefore, the LTF-based channel estimation method is appropriate for be used in a slow fading channel environment in which the channel changes infrequently, whereas the pilot-based channel estimation method is appropriate for be used in a fast fading channel environment in which the channel changes frequently. However, a channel estimation method in wireless communication network of the IEEE 802.11ad communication standard cannot use a fixed specific channel environment in view of the characteristics of a high-speed channel environment using a broad bandwidth in performing a short-range wireless communication.